This unusual fighter plane McDonnell XF-85 Goblin was designed to meet a USAAF requirement for a single-seat "parasite" escort fighter that could be carried by a large bomber. Development of two prototypes was ordered in March 1947. The resulting design was entirely the product of design constraints, which required it to fit into the bomb bay of a B-36 (although it was actually tested under a B-29). The B-36 was the intended mother ship that would carry as many as three Goblins.

A tiny, short fuselage was fitted with low/mid-set foldable swept wings, of 21 ft 1.5 in (6.44 m) span. It was powered by a Westinghouse J34-WE-7 turbojet, of 3,000 lb. (1,361 kg) thrust. There was no landing gear except for emergency skids. The fighter was intended to return to the parent aircraft and dock with a trapeze, by means of a retracting hook.